This invention relates to a motor vehicle which is powered by an internal combustion engine mounted in an engine compartment. The latter is provided with additional encapsulating elements sealed against parts of the frame and body of the vehicle, to form a sound-insulating capsule comprising sound-absorbing inlet and outlet openings for ventilation of the capsule. At least one of these openings is located in the area where the heated air rises from the exhaust system of the engine, and cooperates with a separate exhaust casing mounted within the capsule.
Today, internal combustion engines--especially those powering motor vehicles used on public motorways--must meet ever more stringent demands concerning the maximum permissible sound radiation. Conventional sound-proofing techniques range from the partial coating with sound-insulating materials and the de-coupling of individual non-power-transmitting components from the basic structure of the combustion engine carrying structure-borne sound, to the use of complete capsules enclosing the combustion engine and even some auxilliary assemblies, thus reducing the radiation of sound from the internal combustion engine.
Since a comparatively large amount of heat is generated by an internal combustion engine in operation, such closed capsules--even if they contain a water-cooled engine--should only be used if the space remaining between the surface of the engine and the wall of the capsule is properly ventilated in order to prevent delicate components, e.g., the dynamo, from overheating. Although it would basically be possible to locate such components outside of the capsule, this would cause problems regarding the power transmission to these components or the penetration of the necessary leads and ducts through the capsule.
In this context special attention must be paid to the exhaust system of the combustion engine, which is not only a source of extreme noise--at least in the vicinity of the cylinder head--but is also one of the hottest parts of the engine, reaching temperatures which necessitiate that the air heated by the exhaust system must be able to flow out of the capsule even after the engine has been turned off. This may be achieved in several ways, as described below.